Ophthalmologists employ a wide variety of tools in examining eye conditions and assessing potential ocular damage and disease states. Testing and examination of the human eye is a particularly difficult process as the eye is a very fragile structure and is often sensitive to even the most benign compositions. Furthermore, the membranes around the eye and the ocular tissue are easily contaminated with infectious agents and provide a natural and effective growth media for these agents upon contact. This makes the design and implementation of examination procedures particularly difficult.
A well-known test commonly performed by ophthalmologists is referred to as applanation tonometry. This is a technique for assessing intra-ocular pressure with minimal intrusion to the patient. The evaluation of intra-ocular pressure is used to ascertain the existence of certain ocular problems such as glaucoma, that are evidenced by increased intraocular pressure. Applanation tonometry is practiced in a number of ways and is described in more detail in the following references--the contents of which are hereby incorporated by reference thereto as if restated here in full; see, specifically, "Recommendations for Ophthalmic Practice in Relation to the Human Immunodeficiency Virus" pages 1-6, Vol. 5/Chap. 64 of CLINICAL OPHTHALMOLOGY; "APIC Guidelines for Infection Control Practice" pages 99-117, Vol. 18/No. 2, of the April 1990, issue of AMERICAN JOURNAL OF INFECTION CONTROL; "Goldmann Tonometry and Fluorescein Solution: A Way to Avoid Contact Lens Staining" pages 61-62, 324-327 of the October, 1991, issue of CLAO JOURNAL; "The ophthalmic rod: a new ophthalmic drug delivery system I" pages 297-301 of the 1990, issue of GRAEFE'S ARCHIVE CLINICAL AND EXPERIMENTAL OPHTHALMOLOGY; "The ophthalmic rod: a new drug-delivery system II" pages 302-304 of the 1990, issue of GRAEFE'S ARCHIVE CLINICAL AND EXPERIMENTAL OPHTHALMOLOGY. The common procedure in applanation tonometry and tonometers in use requires the placement of a small amount of a staining agent, often fluorescein, onto the ocular tissue and contacting this tissue with a planar (applanations) lens surface to create a meniscus on the lens surface. As can be seen in FIG. 1, the capillary action of the fluid (25) between the lens (5) and the cornea tissue (15) forms a circular region the attributes of which in part are determined by the ocular pressure. These attributes include the angle that is formed by the meniscus and the contact area (35) of the lens to the cornea. By aligning the prism lens in the tonometer, the ophthalmologist gains information about ocular pressure.
As with most ocular examinations, there is significant concern about preventing infection to the ocular tissue when using the tonometer. The tonometer lens is made of a fragile polymer material that precludes the use of autoclaves or other heat based disinfecting processes or strong caustic solutions for disinfection, as these may craze or cloud the lens surface. Therefore, it is the common practice to apply a milder disinfectant onto the tip of the tonometer just prior to its use. The disinfectant that is typically used for this application is a seventy (70%) percent isopropyl alcohol, although ethyl alcohol also can be used. The disinfectant is applied by wiping the lens surface with a sponge containing the disinfectant. This procedure is considered sufficient to sterilize the tonometer from HIV and HBV viruses, but there remains some questions as whether this procedure is sufficient to sterilize the lens from adenovirus and other non-lipid (hydrophilic) viral agents.
In addition to the tonometer, the fluorescein solutions used in conjunction therewith must be provided in a sterile manner. Most ophthalmic solutions suppress bacterial growth with one or more preservatives--illustrative examples including benzalkonium chloride, chlorobutanol and chlorhexidine. However, fluorescein solutions are especially susceptible to bacterial infection. Because of this, a separate mechanism has been developed and is in use for its delivery. Fluorescein is stored on dry filter paper--just prior to dispensing the fluorescein, the filter paper is wetted with a sterile aqueous saline solution. Once placed in solution, the fluid is instilled into the conjunctival cul-de-sac, followed immediately by the initiation of the applanation procedure.
The foregoing procedures are difficult and time consuming to implement. Indeed, there have been many efforts to enhance sterile delivery of medicants to the eyes and significant research in this area. For example, in 1989, several papers were published on the use of an "ophthalmic rod" for the introduction of infection free medicants. See specifically, the articles [Insert references] the contents of which are herein incorporated by reference as if restated in full. This approach applies a dried medicant on the end of the thin rod which is then subjected to Gamma radiation--to insure complete destruction of any residual infectious agents. However, such a procedure has problems of its own and cannot be readily implemented for tonometry.
There has remained a need to enhance the examination procedure practiced by eye care specialist during the use of applanation tonometry. The present invention is directed to addressing this continuing need.